Conventionally, there has been a ball bearing cage described in JP 2001-304268 A. The ball bearing cage is formed by rivet connecting same two wave-shaped annular plate members of an alternate succession of semicircular portions and flat portions. The wave-shaped annular plate members are formed by press forming annular metal plate members, and one through hole is formed generally at the center of each flat portion of the annular plate members. After the two wave-shaped annular plate members are placed facing each other so that the through holes of the two wave-shaped annular plate members face each other, a rivet is inserted penetrating the two through holes whose openings are brought in contact with each other, and end face of the rivet inserted through the through hole and located on the opposite side of the head portion are beaten by a hammer or a rivet gun, connecting the two wave-shaped annular plate members together. When the two wave-shaped annular plate members are connected together, the semicircular portion of one wave-shaped annular plate member and the semicircular portion of the other wave-shaped annular plate member conjointly form a generally cylindrical circumferentially inner surface. The generally cylindrical inner surface constitutes a pocket to accommodate a ball. The ball bearing cage has the advantages that it can be manufactured simply at low cost and has excellent heat resistance since it is made of metal.
However, the conventional ball bearing cage is rigid with poor flexibility although it has excellent heat resistance. When the ball bearing is used under momental load conditions and hard acceleration and deceleration conditions, moving differences, i.e., lead and lag occur among individual balls. When the ball bearing including the conventional rigid ball bearing cage is used under the momental load conditions and the hard acceleration and deceleration conditions as described above, the cage cannot follow the lead and lag of the balls with its elastic deformation, and the balls and the inner circumferential surfaces of the pockets of the ball bearing cage are brought in intense contact with each other. There is a problem that a tensile force and a compressive force are generated between adjoining pockets due to the intense contact, causing the occurrence of tear of break or the like particularly in proximate portions including boundaries between the semicircular portions and the flat portions located between adjoining pockets of the ball bearing cage and in neighborhood portions including the through holes through which the rivets penetrate and seizure between the balls and the inner circumferential surfaces of the pockets. Moreover, the inertial force of the cage is great due to its mass, and this also influences the torque of the ball bearing.
If the thickness of the plate member is increased to prevent the tear of break or the like, the strength of the cage can be increased, while there is a problem that the form accuracy of the surfaces that hold the balls is degraded and the contact between the cage and the balls becomes nonuniform. Moreover, there is a problem that the manufacturing cost of the cage is increased and the weight and the axial dimension of the cage are increased. On the other hand, the conventional ball bearing cage has a problem that the tear of break or the like occurs in the cage since mechanical characteristics of tensile strength, fatigue strength and so on of the cage become insufficient when the thickness of the plate member is reduced although the axial dimension of the cage can be reduced to allow the cage to be reduced in weight, improved in torque characteristics and improved in flexibility.
Further, a resin-made cage formed of polyamide 66 or the like has also conventionally been known. The resin-made cage generally has heat resistance inferior to that of one made of metal (particularly made of steel) although it has excellent flexibility and light weight, and, for example, polyamide 66 practically has a use upper limit temperature of about 120° C. Even a heat-resistant resin has, for example, a use upper limit temperature of about 200° C. and is also very expensive. Moreover, the resin-made cage also has a problem that it is deteriorated by oil components and additives of a lubricant and degraded in strength. Moreover, it is also known that the resin-made cage generates a weld when manufactured by injection molding and easily breaks at the portion. Resin has a coefficient of linear expansion greater than that of metal (particularly steel) and ceramic. When a resin-made cage is incorporated into a ball bearing, the ball bearing causes torque fluctuations, generation of noises and generation of vibrations due to changes in clearance caused by temperature changes.
Moreover, there has conventionally been a roller bearing cage described in JP 2005-048834 A. The cage is made of a metal plate member and forms pockets that accommodate tapered rollers by connecting a minor diameter annular portion and a major diameter annular portion with a plurality of bar portions. The cage has excellent heat resistance since it is made of the metal plate member. An outer end portion in the axial direction of the minor diameter annular portion is bent inward in the radial direction. The conventional tapered roller bearing secures the strength in the radial direction of the cage by bending the outer end portion in the axial direction of the minor diameter annular portion inward in the radial direction. However, there is a problem that, when the cage is reduced in thickness for the demand of reducing the weight of the cage, the strength is insufficient only by bending the minor diameter annular portion.
Moreover, the cage becomes rigid when increased in thickness similar to or further than in the conventional case in order to maintain the strength of the cage. When the roller bearing is used under momental load conditions and hard acceleration and deceleration conditions, lead and lag of rollers occur. However, when a roller bearing in which a rigid cage is incorporated is used under momental load conditions and hard acceleration and deceleration conditions, the cage cannot follow the lead and lag of the rollers, and the rollers and the inner circumferential surfaces of the pockets of the cage are brought in intense contact with each other. There is a problem that seizure occurs between the rollers and the pockets of the cage and the cage is broken by a tensile force and a compressive force generated between adjoining pockets due to the intense contact.
Moreover, there is a problem that, when the roller bearing cage is a needle roller bearing cage, the cage has a very weak strength since the axial end portion cannot be bent in the radial direction.
Further, a resin-made cage formed of polyamide 66 or the like has also conventionally been known. The resin-made cage generally has heat resistance inferior to that of one made of metal (particularly made of steel) although it has excellent flexibility and light weight, and, for example, polyamide 66 practically has a use upper limit temperature of about 120° C. Even a heat-resistant resin has, for example, a use upper limit temperature of about 200° C. and is also very expensive. Moreover, the resin-made cage also has a problem that it is deteriorated by oil components and additives of a lubricant and degraded in strength. Moreover, it is also known that the resin-made cage generates a weld when manufactured by injection molding and easily breaks at the portion. Resin has a coefficient of linear expansion greater than that of metal (particularly steel) and ceramic. When a resin-made cage is incorporated into a roller bearing, the roller bearing causes torque fluctuations, generation of noises and generation of vibrations due to changes in clearance caused by temperature changes.
It is an object of the present invention to provide a rolling bearing cage, which is compact and has great strength and excellent flexibility, heat resistance and oil resistance. It is a particular object to provide a ball bearing cage, which has a small axial dimension of the cage, light weight, great strength and hardness, and excellent flexibility, heat resistance, oil resistance and abrasion resistance, and a ball bearing that has the ball bearing cage. Another particular object is to provide a roller bearing cage, which is lightweight and compact and has great strength and excellent flexibility, heat resistance and oil resistance, and a roller bearing that has the roller bearing cage.